Nondestructive inspection apparatus for inspecting an internal defect in an object

ABSTRACT

A nondestructive inspection apparatus includes a vibrating section  11  which is adapted to be placed in pressure contact with a surface of a measuring object  16  for generating an acoustic elastic wave W, a receiving section  12  for receiving a reflected wave, a pushing mechanism  13  for pushing the vibrating section and the receiving section against the measuring object, a pushing force measurement section  14  for detecting pushing forces Fa, Fb during vibration, a vibration control section  10  for driving the vibrating section, and a reception signal processing section  15  for determining the internal defect based on a reception signal R. The reception signal processing section includes a reflection energy calculation section for calculating a reflection energy level due to elasticity vibration of the measuring object, a reflection energy correction section for normalizing the reflection energy level by the pushing force to calculate a correction value; and an internal defect determination section for detecting the internal defect based on the correction value. With this arrangement, the absolute reflection energy level of the reflected wave is determined through comparison, thereby making it possible to improve the evaluation accuracy of the internal defect to a substantial extent.

TECHNICAL FIELD

The present invention relates to a nondestructive inspection apparatuscapable of inspecting an internal defect existing in a measuring objectsuch as a concrete structure, and more particularly it relates to anondestructive inspection apparatus which enables the diagnosis ofinternal defects with high reliability by correcting the reflectionenergy level of an acoustic elastic wave in the form of a vibration wavewith high accuracy.

BACKGROUND ART

In the past, hammering tests from an external surface using a hammerhave been widely practiced in order to detect internal defects existingin a concrete structure for instance for the reason of convenience andfacilitation.

However, when such a well-known hammering test method is used, theaccuracy of tests depends on the operator's ability and the level of hisor her skill, and it is extremely difficult to carry out hammering by aconstant force at all times. In addition, there has been a problem inthat the criterion for determination depends greatly on the operator'sexperience and intuition, so the result of diagnosis becomes vague,making it impossible to achieve sufficient reliability.

Thus, in order to obviate the above problem, there have been proposed avariety of kinds of improved nondestructive inspection apparatuses.

FIG. 11 is a block diagram illustrating a known nondestructiveinspection apparatus described for instance in Japanese PatentApplication Laid-Open No. 8-21824 to which a method of inspectingdefective fillings is applied.

In FIG. 11, the nondestructive inspection apparatus includes a wavetransmitting probe 111 which constitutes an acoustic wave transmittingsection, a wave receiving probe 112 which constitutes an acoustic wavereceiving section, a survey unit 113 having an acoustic wavetransmitter, and an FFT analyzer 114 which executes calculationprocessing by using fast Fourier transform.

Also, a nondestructive inspection object (i.e., an object to besubjected to nondestructive inspection) is provided with a plate member120 against which the wave transmitting probe 111 and the wave receivingprobe 112 are adapted to be placed into abutment, and a filler 130 suchas concrete, etc., arranged in the plate member 120. The filler 130includes a filling defective portion 131 such as a crack, a void, etc.,as shown in FIG, 11.

Now, reference will be made to a method of inspecting defective fillingscarried out according to the known nondestructive inspection apparatusillustrated in FIG. 11.

First of all, the wave transmitting probe 111 for acoustic wavetransmission and the wave receiving probe 112 for acoustic wavereception are placed into abutment against a surface of the plate member120, as shown in FIG. 11, and an acoustic wave having a wide-bandfrequency component is repeatedly transmitted from the survey unit 113through the wave transmitting probe 111.

As a result, the acoustic wave transmitted from the wave transmittingprobe 111 is repeatedly sent from the surface of the plate member 120toward the filler 130.

The wave receiving probe 112 receives a reflected wave of the acousticwave transmitted from the wave transmitting probe 111 and converts itinto a corresponding electric signal, which is then input to the FFTanalyzer 114 through the survey unit 113.

The FFT analyzer 114 carries out Fourier analysis of the receptionsignal and outputs a frequency spectrum level thus obtained to a CRTdisplay (not shown), etc.

Accordingly, an operator can measure the frequency spectrum level outputby the FFT analyzer 114 so as to determine the presence or absence ofthe filling defective portion 131.

With the known nondestructive inspection apparatus as constructed above,if each of the probes 111, 112 is not in contact with the surface of theplate member 120, which acts as a measuring surface, in a satisfactorymanner, there would be generated attenuation of the acoustic elasticwave between the wave transmitting probe 111 (vibrating section) or thewave receiving probe 112 (receiving section) and the contact surface(measuring surface) of the plate member 120, thus making it difficult toaccurately measure the reflection energy level.

Particularly, the surface condition of the concrete structure isvariously changed depending upon the environment where it is placed, sothere will likely arise a situation that each of the probes 111, 112 isnot able to contact the measuring surface to any satisfactory extent.Such a situation may be considered to include the cases wherein themeasuring surface is rugged, or is deteriorated by weathering, or isattached by dust or the like for example.

Moreover, in cases where the respective probes 111, 112 are manuallypushed against the measuring surface, the ruggedness of the measuringsurface and the condition of attachment of foreign matters greatlyinfluence the contact forces, thereby further reducing the accuracy ofmeasurements by the use of the level of the reflected wave.

In addition, with the known nondestructive inspection apparatus, incases where a measuring object is changed, or the condition of thecontact surface varies with the lapse of time, it would be impossible tomake comparison of reflected waves, and hence it has been difficult toevaluate different objects through comparison or by following or tracingchanges thereof over time.

Furthermore, since the reflection energy level of the reflected wavecannot be compared by using a constant criterion, there has been aproblem that it is impossible to determine a correlation between thedistance of the filling defective portion 131 of the filler 130 to thereflection surface and the reflection energy level.

The present invention is intended to obviate the problems as referred toabove, and has for its object to provide a nondestructive inspectionapparatus which can infer the condition of the contact of a vibratingsection and a receiving section with a measuring surface thereby tocorrect a criterion, and enable the comparison of the absolutereflection energy level even if there is poor contact of the vibratingsection and the receiving section with the measuring surface, thussubstantially improving the accuracy of measurement of the reflectionenergy level irrespective of the surface condition of a measuring objectand at the same time making it possible to calculate the distance of aninternal defect in the measuring object from the measuring surfacethereof by using a correlation between the distance from the surface toa filling defective portion (internal defect) in the measuring objectand the reflection energy level.

DISCLOSURE OF THE INVENTION

The present invention resides in a nondestructive inspection apparatusfor diagnosing an internal defect of a measuring object by injecting anacoustic elastic wave into the measuring object, the apparatuscomprising: a vibrating section which is adapted to be placed inpressure contact with a surface of the measuring object for generatingthe acoustic elastic wave; a receiving section which is adapted to beplaced in pressure contact with a surface of the measuring object forreceiving a reflected wave of the acoustic elastic wave; a pushingmechanism for pushing the vibrating section and the receiving sectionagainst the surface of the measuring object; a pushing force measurementsection for detecting pushing forces of the vibrating section and thereceiving section against the surface of the measuring object duringvibration thereof; a vibration control section for driving the vibratingsection thereby to generate the acoustic elastic wave; and a receptionsignal processing section for determining the internal defect based onthe reception signal from the receiving section; wherein the receptionsignal processing section comprises: a reflection energy calculationsection for calculating a reflection energy level due to elasticityvibration of the measuring object based on the reception signal; areflection energy correction section for normalizing the reflectionenergy level by the pushing force to calculate a correction value; andan internal defect determination section for detecting the internaldefect based on the correction value.

Moreover, the vibrating section according to the nondestructiveinspection apparatus of the present invention includes amagnetostrictive vibrator for generating the acoustic elastic wavethrough a magnetostriction phenomenon.

In addition, the acoustic elastic wave according to the nondestructiveinspection apparatus of the present invention comprises a chirp wavewith its frequency continuously changing with time; the reception signalprocessing section includes an envelope detecting section fordetermining an envelope of elasticity vibration caused by the reflectionof the chirp wave, the envelope detecting section being operable tocalculate, based on the envelope, a resonance frequency according to anatural oscillation characteristic of the measuring object; and theinternal defect determination section detects the internal defect basedon the resonance frequency and a response waveform of the supplyfrequency.

Further, the internal defect determination section according to thenondestructive inspection apparatus of the present invention calculatesa distance to the internal defect based on a correlation between adistance to the internal defect and the correction value which isprepared in advance.

Furthermore, the correlation between the distance to the internal defectand the correction value according to the nondestructive inspectionapparatus of the present invention is stored in advance in the internaldefect determination section as map data of actual measurement valuescorresponding to the measuring object.

Still further, the reflection energy correction section according to thenondestructive inspection apparatus of the present invention calculatesan additional correction value by dividing the correction value by anabnormal range area of the internal defect; and the internal defectdetermination section calculates the distance to the internal defectbased on a correlation between the distance to the internal defect andthe additional correction value which is prepared in advance.

Moreover, the correlation between the distance to the internal defectand the additional correction value according to the nondestructiveinspection apparatus of the present invention is stored in advance inthe internal defect determination section as map data of actualmeasurement values corresponding to the measuring object.

In addition, the measuring object according to the nondestructiveinspection apparatus of the present invention comprises a concretestructure.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram illustrating a first embodiment of the presentinvention.

FIG. 2 is a block diagram illustrating a vibration control sectionaccording to the first embodiment of the present invention.

FIG. 3 is a perspective view illustrating a vibrating section accordingto the first embodiment of the present invention.

FIG. 4 is a block diagram illustrating a reception signal processingsection according to the first embodiment of the present invention.

FIG. 5 is a characteristic view illustrating the correlation between apushing force and a reflection energy level according to the firstembodiment of the present invention.

FIG. 6 is a block diagram illustrating a vibration control sectionaccording to the second embodiment of the present invention.

FIG. 7 is a waveform view illustrating an acoustic elastic wave outputfrom the vibration control section according to the second embodiment ofthe present invention.

FIG. 8 is a block diagram illustrating a reception signal processingsection according to the second embodiment of the present invention.

FIG. 9 is a characteristic view illustrating the correlation between thedistance to an internal defect detected and a reflection energy levelcorrection value in relation to a third embodiment of the presentinvention.

FIG. 10 is a characteristic view illustrating the correlation betweenthe distance to an internal defect measured and a reflection energylevel additional correction value in relation to a fourth embodiment ofthe present invention.

FIG. 11 is a block diagram illustrating a known nondestructiveinspection apparatus.

THE BEST MODE FOR IMPLEMENTING THE INVENTION Embodiment 1

Hereinafter, a first embodiment of the present invention will bedescribed based on the accompanying drawings.

FIG. 1 is a block diagram illustrating the first embodiment of thepresent invention.

In FIG. 1, a nondestructive inspection apparatus according to thepresent invention includes a vibration control section 10 for generatinga drive signal W to produce an acoustic elastic wave of an audiblefrequency region, a vibrating section 11 for generating the acousticelastic wave according to the drive signal W, a receiving section 12having a reception sensor for detecting a reflected wave of the acousticelastic wave, a pushing mechanism 13 provided on the rear ends of thevibrating section 11 and the receiving section 12, pushing forcemeasurement sections 14 each having a pressure sensor for detectingpushing or urging forces Fa, Fb at the tip ends of the vibrating section11 and the receiving section 12, respectively, and a reception signalprocessing section 15 for performing calculation or arithmeticprocessing of a reception signal R from the receiving section 12.

The measuring object 16 has an internal defect 17 (void, crack, peelingoff, etc.) corresponding to the above-mentioned filling defectiveportion 131 (see FIG. 11), and the vibrating section 11 and thereceiving section 12 are pushed or pressed against a surface (measuringsurface) of the measuring object 16 by the pushing or urging force ofthe pushing mechanism 13.

The pushing or urging forces Fa, Fb of the vibrating section 11 and thereceiving section 12 during vibration are detected by the pushing forcemeasurement sections 14, and input to the reception signal processingsection 15 together with the reception signal R.

Here, note that the pushing forces Fa, Fb are adjusted to become anequal pushing force F with each other.

Moreover, measurement gauges or the like for measuring the pushingreactive forces at the tip ends of the vibrating section 11 and thereceiving section 12 for instance are used as the pushing forcemeasurement sections 14.

In addition, a display (not shown) for displaying the result ofdetermination about the internal defect 17, etc., is connected with thereception signal processing section 15.

FIG. 2 is a block diagram illustrating a concrete example of thevibration control section 10 in FIG. 1.

In FIG. 2, the vibration control section 10 includes a vibration wavegeneration section 10 a for generating a drive signal W to the vibratingsection 11, and a power amplifier 10 b for amplifying the drive signal Wfrom the vibration wave generation section 10 a and imposing it on thevibrating section 11.

FIG. 3 is a perspective view illustrating a concrete example of theconfiguration of the vibrating section 11 in FIG. 1.

In FIG. 3, the vibrating section 11 is provided with a magnetostrictivevibrator 11 a in the shape of a closed-loop core constituted bylaminated magnetostrictive elements, and excitation windings 11 b woundround two opposed side portions of the magnetostrictive vibrator 11 a.The magnetostrictive vibrator 11 a vibrates in a direction passingthrough two sides (see an arrow) of the vibrating section 11 aroundwhich the excitation windings 11 b are not wound.

FIG. 4 is a block diagram illustrating a concrete example of thereception signal processing section 15 in FIG. 1.

In FIG. 4, the reception signal processing section 15 includes areflection energy calculation section 15 a for calculating a reflectionenergy level Er based on the reception signal R of the reflected wave, areflection energy correction section 15 b for correcting the reflectionenergy level Er by using the pushing forces Fa, Fb, and an internaldefect determination section 15 c for determining the presence orabsence of an internal defect based on a corrected reflection energylevel correction value Ec.

FIG. 5 is a characteristic view illustrating the correlation between thereflection energy level Er and the pushing force F according to thefirst embodiment of the present invention, the correlation being storedin advance as map data in the reflection energy correction section 15 bfor instance.

In FIG. 5, the axis of abscissa represents the pushing force F [MPa],and the axis of ordinate represents the reflection energy level Er [mV].

Next, reference will be made to the operation of the first embodiment ofthe present invention while referring to FIG. 1 through FIG. 5.

In FIG. 1, first of all, the vibration control section 10 drives thevibrating section 11 by means of a drive signal W (a drive current of apredetermined frequency) to generate an acoustic elastic wave.

The vibration control section 10 is comprised of the vibration wavegeneration section 10 a and the power amplifier 10 b, as illustrated inFIG. 2, and the vibration wave generation section 10 a generates acurrent waveform in a band corresponding to the characteristic frequency(determined in accordance with the materials of the measuring object 16,the distance to the internal defect 17 therein, etc.), and outputs thisto the power amplifier 10 b as the drive signal W.

The power amplifier 10 b amplifies the drive signal W and outputs it byadjusting the drive signal W to a current value (or voltage value)suitable for driving the vibrating section 11.

The vibrating section 11 is comprised of the magnetostrictive vibrator11 a which forms a core, and the excitation windings 11 b which generatea magnetic field in the magnetostrictive vibrator 11 a, as illustratedin FIG. 3, and the magnetostrictive vibrator 11 a has such acharacteristic as to cause a distortion (magnetostriction phenomenon)according to the magnitude and frequency of the magnetic fieldgenerated.

Accordingly, when the drive signal W is imposed on the excitationwindings 11 b, there is generated a magnetic field in themagnetostrictive vibrator 11 a so that the magnetostrictive vibrator 11a generates an acoustic elastic wave under the action of theabove-mentioned magnetostriction phenomenon.

At this time, the response speed of the magnetostrictive vibrator 11 ato a change in the magnetic field is several micro seconds or less, andhence it is within a range in which the magnetostrictive vibrator 11 acan follow or trace a current change in an audible frequency range.

Moreover, an acoustic elastic wave of this frequency band can beefficiently generated by supplying a drive signal W in the audiblefrequency range.

In addition, the magnitude of the magnetic field generated in thevibrating section 11 changes depending on the magnitude and thefrequency of the imposed drive signal W, so the amount of distortion ofthe magnetostrictive vibrator 11 a can be adjusted by controlling thecurrent value of the drive signal W.

The core of the vibrating section 11 (magnetostrictive vibrator 11 b inFIG. 3) is caused to generate a distortion in accordance to the currentvalue of the imposed drive signal W, whereby an acoustic elastic wave(vibration wave) is injected into the measuring object 16 from thecontact portion of the core with the measuring object 16.

The acoustic elastic wave injected from the vibrating section 11diffuses while being attenuated under the damping effect duringpropagation in the measuring object 16.

When the acoustic elastic wave during the propagation in the measuringobject 16 reaches an acoustic reflection surface of the internal defect17 (foreign matter, crack, etc.), it is reflected by and penetratesthrough an interface of the acoustic reflection surface.

In the interface of such an acoustic reflection surface, the greater thecontrast of the acoustic propagation speed, it becomes more difficultfor the acoustic elastic wave to penetrate, so there is developed alarge reflection wave. For instance, in the case of a crack or voidwhich is in contact with air at the back side of the acoustic reflectionsurface, the most amount of energy of the acoustic elastic wavepropagated is reflected at the interface.

On the other hand, in the case of the measuring object 16 within whichthere exists no acoustic reflection surface, the acoustic elastic waveinjected from the measuring surface propagates in the interior of themeasuring object 16 so that reflection waves are generated at theopposed surface of the measuring surface and the side surfaces of themeasuring object.

In this manner, the reflected waves, which have propagated through theinterior of the measuring object 16 to be reflected from the opposedsurface and the side surfaces thereof, have been influenced by theattenuation and diffusion of the acoustic elastic wave more greatly thanthe reflected wave from the internal defect 17 has. As a result, theamplitude of the reflected wave from the measuring object 16 without anyinternal defect 17 becomes smaller than that in the case where thereexists a reflection surface (internal defect 17) inside the measuringobject.

Thus, the receiving section 12 is made into contact with a surface(measuring surface) of the measuring object 16 to detect a reflectedwave from the acoustic reflection surface, whereby it is possible todetermine the presence or absence, the magnitude, etc., of an acousticreflection surface (internal defect 17).

That is, the reflection energy calculation section 15 a in the receptionsignal processing section 15 performs the time integration of thereception signal R to provide a reflection energy level Er, and thereflection energy correction section calculates a reflection energylevel correction value Ec.

Therefore, the internal defect determination section 15 c can determinewhether an acoustic reflection surface exists in the interior of themeasuring object, by making a comparison between the case of thepresence of the internal defect 17 (acoustic reflection surface) and thecase of the absence thereof based on the reflection energy levelcorrection value Ec.

However, there is a correlation between the pushing forces F (Fa, Fb) ofthe vibrating section 11 and the receiving section 12 against thesurface of the measuring object 16 and the reflection energy level Erbased on the reception signal R, as illustrated in FIG. 5.

As is clear from FIG. 5, the reflection energy level Er changes like alinear function according to the pushing forces F, and when the pushingforces F are not sufficient, the expected reflection energy level Er cannot be observed, and hence it is impossible to accurately determine thereflection energy level Er corresponding to the actual reflection wave.

Accordingly, the vibrating section 11 and the receiving section 12 areurged or pushed against the surface (measuring surface) of the measuringobject 16 by means of the pushing mechanism 13, and the contactpressures (pushing forces F) between the vibrating section 11 and thereceiving section 12 and the measuring surface are measured by thepushing force measurement sections 14, and the results of themeasurements are input to the reception signal processing section 15,whereby it becomes possible for the reception signal processing section15 to carry out the estimating or inferring calculation of thereflection energy level correction value Ec normalized according to thepushing forces F.

As a result, the reflection energy level Er can be corrected by usingthe values of the pushing forces F even if there are not generatedenough pushing forces F, thus making it possible to estimate or inferthe reflection energy level correction value Ec.

That is, the reception signal processing section 15 corrects throughnormalization the reflection energy level Er by the pushing forces Fbased on the reception signal R and the pushing forces F, and makes adetermination of the internal defect 17 based on the reflection energylevel correction value Ec.

First of all, the reflection energy calculation section 15 a in thereception signal processing section 15 (see FIG. 4) calculates thereflection energy level Er detected by the receiving section 12, andinputs the result of the calculation to the reflection energy correctionsection 15 b.

The reflection energy correction section 15 b corrects the reflectionenergy level Er by using the pushing forces F of the vibrating section11 and the receiving section 12 (the value of Fa or Fb) measured by thepushing force measurement sections 14, and inputs the reflection energylevel correction value Ec to the internal defect determination section15 c.

The internal defect determination section 15 c informs the operator ofthe determination result by displaying it from the characteristic of theinternal defect 17 prepared in advance, based on the reflection energylevel correction value Ec.

In this manner, by estimating and correcting the extent or degree ofcontact of the vibrating section 11 and the receiving section 12 withthe measuring surface based on the pushing forces F, it is possible todetermine through comparison the absolute reflection energy level of theacoustic elastic wave irrespective of the surface condition of themeasuring object 16. Thus, the accuracy in the evaluation of theinternal defect 17 based on the reflection energy level correction valueEc can be greatly improved.

Embodiment 2

A mere acoustic elastic wave has been used as a vibration wave in theabove-mentioned first embodiment, but instead there may be used anacoustic elastic wave comprising a chirp wave of which the frequency ischanged over time.

FIG. 6 is a block diagram illustrating a vibration control section 10for generating a chirp wave as an acoustic elastic wave, wherein thesame or like components as those in the aforementioned embodiment (seeFIG. 2) are identified by the same symbols while omitting a detaileddescription thereof.

In FIG. 6, a chirp wave generation section 10 c corresponds to theabove-mentioned vibration wave generation section 10 a, and serves togenerate a drive signal W comprising a chirp wave.

FIG. 7 is a waveform view illustrating the drive signal W (chirp wave)output from the vibration control section 10 to the vibrating section11.

In FIG. 7, the axis of abscissa represents time t, and the axis ofordinate represents the current value of the drive signal W, wherein thefrequency of the drive signal W comprising the chirp wave continuouslyincreases with the lapse of time t. Incidentally, contrary to FIG. 7,there can be used a chirp wave of which the frequency continuouslydecreases with the lapse of time.

FIG. 8 is a block diagram illustrating a reception signal processingsection 15 for processing a reception signal R based on a reflectionwave of the chirp wave, wherein the same or like components as those inthe aforementioned embodiment (see FIG. 4) are identified by the samesymbols while omitting a detailed description thereof.

In FIG. 8, an envelope detecting section 15 d corresponds to theabove-mentioned reflection energy calculation section 15 a, and servesto calculate an envelope of the reception signal R as a reflectionenergy level, which is input to the reflection energy correction section15 b.

Now, reference will be made to the operation of the second embodiment ofthe present invention while referring to FIG. 6 through FIG. 8 alongwith FIG. 1 and FIG. 3.

First of all, the chirp wave generation section 10 c in the vibrationcontrol section 10 inputs a drive signal W (chirp wave), of which thefrequency continuously rises with the lapse of time, to the poweramplifier 10 b, and the power amplifier 10 b properly amplifies thecurrent waveform of the chirp wave and imposes it on the vibratingsection 11 for driving thereof.

The magnetostrictive vibrator 11 a of the vibrating section 11 (see FIG.3) generates a distortion according to the current waveform of theimposed drive signal W, whereby an acoustic elastic wave, of which thefrequency rises (or lowers) continuously with time t, is injected into ameasuring object 16 at a constant magnitude from the surface of themeasuring object 16 which is contacted by the magnetostrictive vibrator11 a.

In this manner, in cases where vibration due to the acoustic elasticwave is given to the measuring object 16, the amplitude of the waveformof the reception signal R observed by the receiving section 12 becomesgreat when the excitation or vibration frequency is consistent with anatural resonance frequency of the measuring object 16, whereas theamplitude of the waveform of the reception signal R for the frequenciesother than this becomes small. That is, the waveform of the receptionsignal R, of which the amplitude level varies according to the responsecharacteristic of the natural vibration of the measuring object 16, isobserved by the receiving section 12.

Since the variation in the amplitude level is proportional to thefrequency response of the measuring object 16, a frequency responsewaveform inherent to the measuring object 16 is obtained by calculatingthe envelope of the waveform of the observed reception signal R.

The resonance frequency inherent to the measuring object 16 is observedas a predominant frequency as seen in the frequency response, so thatone can know the form of vibration at the measuring surface byextracting a peak frequency of the reception signal R. Accordingly, theinternal defect 17 in the measuring object 16 and its structure per secan be estimated from the envelope of the waveform of the receptionsignal R, and discrimination can be easily made between a normal portionand an abnormal portion of the measuring object 16.

In FIG. 8, the envelope detecting section 15 d calculates the envelopeof the reception signal R from the receiving section 12 as thereflection energy level Er. The envelope of the reception signal Rrepresents the frequency response waveform of the measuring object 16.Thereafter, the internal defect 17 can be determined based on thereflection energy level correction value Ec corrected by the pushingforces F.

In this manner, by calculating the envelope of the reception signal R asthe reflection energy level Er by the use of an acoustic elastic wavecomprising a chirp wave as a vibration wave, the frequency responsewaveform can be obtained without performing complicated signalprocessing such as FFT (Fast Fourier Transform) by simple and convenientcalculation processing.

Therefore, it is possible to shorten the processing time to asubstantial extent, make wider the inspection area to be inspectedwithin a prescribed period of time, and reduce the size or scale of themeasuring equipment for labor saving.

Embodiment 3

Although in the above-mentioned first and second embodiments, noreference has been made to any concrete parameter which is an object fordetermining the internal defect 17, the distance to the internal defect17 for example may be made such a determination object.

FIG. 9 is a characteristic view illustrating the correlation between thereflection energy level correction value Ec and the distance D to theinternal defect actually measured in relation to a third embodiment ofthe present invention, wherein the correlation is stored in advance inthe internal defect determination section 15 c as map data of themeasurement values corresponding to the measuring object 16.

In FIG. 9, the axis of abscissa represents the distance D to theinternal defect (the thickness of a peeled-off portion, the depth of acrack, etc., measured at the surface of the measuring object 16), andthe axis of ordinate represents the reflection energy level correctionvalue Ec.

The characteristic of FIG. 9 is obtained by acquiring a cross sectionalstructure at a measurement location of the measuring object 16 by coringa concrete structure for instance, actually measuring the distance D tothe internal defect 17 (the depth of a crack, etc.), and actuallymeasuring the reflection energy level Er at the measurement locationthereby to calculate a correction value Ec which is normalized by thepushing forces F during vibration.

As described above, the acoustic elastic wave injected from thevibrating section 11 diffuses while being attenuated by the dampingeffect during propagation through the measuring object 16, but in thisattenuation diffusion process, the influences of attenuation anddiffusion are reduced more greatly for an internal defect 17 (crack orvoid) near the measuring surface than for the ones far away therefromsince the distance of propagation of the acoustic elastic wave becomesshorter for the former than for the latter.

Therefore, the reflected wave from the internal defect 17 near themeasurement surface is detected with a greater amplitude than that withwhich the reflected wave from the internal defect 17 far from themeasuring surface is detected, so the reflection energy level correctionvalue Ec changes in inverse proportion to the distance D to the internaldefect 17, as shown in FIG. 9.

The internal defect determination section 15 c stores the characteristicof FIG. 9 measured in advance or an approximate expression correspondingto the characteristic of FIG. 9, and calculates the distance D to theinternal defect 17 through estimation by using the reflection energylevel correction value Ec normalized by the pushing forces F and thecorrelation of FIG. 9 (approximate expression).

Incidentally, note that the correlation of FIG. 9 is varied depending onthe constituent materials of the measuring object 16, the mixing ratioof the materials, etc., and hence measurements are carried out inadvance to clarify the correlation according to variation in themeasuring object 16.

In this manner, by storing in advance the correlation between thedistance D to the internal defect 17 and the reflection energy levelcorrection value Ec (FIG. 9), it is possible to calculate the distance Dto the internal defect 17 by collating the measurement result of thereflection energy level correction value Ec with the characteristic ofFIG. 9. Thus, the internal defect determination section 15 c can informthe operator of not only the presence or absence of the internal defect17 but also the distance D to the internal defect 17.

Embodiment 4

Although in the above-mentioned third embodiment, the distance D to theinternal defect 17 has been calculated based on the reflection energylevel correction value Ec corrected only by the pushing forces F, such adistance D to the internal defect 17 may be calculated based on anadditional correction value Ecc that is obtained by further correctingthe reflection energy level correction value Ec through division by themagnitude of the internal defect 17 (the area of a measurement region).

FIG. 10 is a characteristic view illustrating the correlation betweenthe distance D to the internal defect actually measured and thereflection energy level additional correction value Ecc in relation to afourth embodiment of the present invention, wherein the correlation isstored in advance in the internal defect determination section 15 c asmap data of the actual measurement values corresponding to the measuringobject 16.

In FIG. 10, the axis of abscissa represents the distance D to theinternal defect, and the axis of ordinate represents the reflectionenergy level additional correction value Ecc.

The characteristic of FIG. 10 is obtained through actual measurementsafter coring as referred to above, and the area of the internal defect17 is obtained as a region indicative of the existence of the internaldefect 17 by repeatedly acquiring the reception signal R while movingthe vibrating section 11 over the surface of the measuring object 16.

In this case, the reflection energy correction section 15 b corrects thereflection energy level Er measured at the surface of the measuringobject 16 by the pushing forces F during vibration, and calculates anadditional correction value Ecc by dividing the thus correctedreflection energy level Er by the area of the part where the internaldefect 17 (peeling off) has been developed.

The greater the area S of the internal defect 17, the greater becomesthe above-mentioned reflection energy level correction value Ec, eventhough the distance D to the internal defect 17 in the measuring object16 of the same materials is constant.

Accordingly, in addition to the reflection energy level correction valueEc, the reflection energy level additional correction value Ecc, whichis obtained by additionally correcting the reflection energy levelcorrection value Ec through division thereof by the area S of theinternal defect 17, has a higher correlation with respect to thedistance D to the internal defect 17.

That is, by dividing the above-mentioned reflection energy levelcorrection value Ec (see FIG. 9) by the area S in which the internaldefect 17 takes place, the characteristic of FIG. 10 is acquired, thusmaking it possible to estimate the distance D to the internal defect 17based on the characteristic of FIG. 10 with further high accuracy.

In this manner, the distance D to the internal defect 17 can beaccurately calculated by further dividing the reflection energy levelcorrection value Ec by the area S of the internal defect 17 to calculatethe additional correction value Ecc and collating the correlation ofFIG. 10 determined in advance.

Since the correlation of FIG. 10 is varied depending on the materials,the mixing ratio or the like of the measuring object 16 as referred toabove, the above-mentioned measurement is performed in order to clarifythe actual correlation.

Although in above-mentioned first through fourth embodiments, thedescription has been made by taking as an example the case in which anacoustic elastic wave generated by a magnetostriction phenomenon isinjected into the measuring object 16 by using the vibrating section 11with the magnetostrictive vibrator 11 a, it goes without saying that thevibrating section 11 is not limited to the magnetostrictive type, butmay be of the piezoelectric type, electrodynamic type or the like whileproviding the same operation and effects as referred to above.

Also, the description has been given to an example in which themeasuring object 16 is a concrete structure, but it is needless to saythat the present invention is applicable to other structures with thesame operation and effects as described above.

INDUSTRIAL APPLICABILITY

As described in the foregoing, the present invention resides in anondestructive inspection apparatus for diagnosing an internal defect ofa measuring object by injecting an acoustic elastic wave into themeasuring object. The apparatus comprises: a vibrating section which isadapted to be placed in pressure contact with a surface of the measuringobject for generating the acoustic elastic wave; a receiving sectionwhich is adapted to be placed in pressure contact with a surface of themeasuring object for receiving a reflected wave of the acoustic elasticwave; a pushing mechanism for pushing the vibrating section and thereceiving section against the surface of the measuring object; a pushingforce measurement section for detecting pushing forces of the vibratingsection and the receiving section against the surface of the measuringobject during vibration thereof; a vibration control section for drivingthe vibrating section thereby to generate the acoustic elastic wave; anda reception signal processing section for determining the internaldefect based on the reception signal from the receiving section. Thereception signal processing section comprises: a reflection energycalculation section for calculating a reflection energy level due toelasticity vibration of the measuring object based on the receptionsignal; a reflection energy correction section for normalizing thereflection energy level by the pushing force to calculate a correctionvalue; and an internal defect determination section for detecting theinternal defect based on the correction value. With this arrangement, itis possible to determine the absolute reflection energy level of thereflected wave through comparison irrespective of the surface conditionof the measuring object, thus improving accuracy in the evaluation ofthe internal defect or flaw to a substantial extent.

In addition, the vibrating section according to the nondestructiveinspection apparatus of the present invention includes amagnetostrictive vibrator for generating the acoustic elastic wavethrough a magnetostriction phenomenon. Thus, the acoustic elastic wavecan be easily injected into the measuring object.

Moreover, the acoustic elastic wave according to the nondestructiveinspection apparatus of the present invention comprises a chirp wavewith its frequency continuously changing with time; the reception signalprocessing section includes an envelope detecting section fordetermining an envelope of elasticity vibration caused by the reflectionof the chirp wave, the envelope detecting section being operable tocalculate, based on the envelope, a resonance frequency according to anatural oscillation characteristic of the measuring object; and theinternal defect determination section detects the internal defect basedon the resonance frequency and a response waveform of the supplyfrequency. With this arrangement, a frequency response waveform can beobtained through simple and convenient processing without performingcomplicated signal processing such as FFT, whereby it is possible toshorten the processing time and realize reduction in scale of themeasuring equipment as well as labor saving.

Further, the internal defect determination section according to thenondestructive inspection apparatus of the present invention calculatesa distance to the internal defect based on a correlation between adistance to the internal defect and the correction value which isprepared in advance. Accordingly, it is possible to detect not only thepresence or absence of an internal defect but also the distance to theinternal defect.

Furthermore, the correlation between the distance to the internal defectand the correction value according to the nondestructive inspectionapparatus of the present invention is stored in advance in the internaldefect determination section as map data of actual measurement valuescorresponding to the measuring object. Thus, the correlation with highaccuracy can be obtained without regard to variations in the measuringobjects, thereby making it possible to further improve reliability inthe result of determination of the internal defect.

Still further, the reflection energy correction section according to thenondestructive inspection apparatus of the present invention calculatesan additional correction value by dividing the correction value by anabnormal range area of the internal defect; and the internal defectdetermination section calculates the distance to the internal defectbased on a correlation between the distance to the internal defect andthe additional correction value which is prepared in advance.Accordingly, the distance to the internal defect can be detected withfurther high accuracy.

Besides, the correlation between the distance to the internal defect andthe additional correction value according to the nondestructiveinspection apparatus of the present invention is stored in advance inthe internal defect determination section as map data of actualmeasurement values corresponding to the measuring object. Thus, it ispossible to obtain the correlation with high accuracy irrespective ofvariations in the measuring objects, whereby reliability in the resultof determination of the internal defect can be further improved.

Moreover, the measuring object according to the nondestructiveinspection apparatus of the present invention comprises a concretestructure. Thus, internal defects or flaws can be effectively determinedin particular for general buildings.

What is claimed is:
 1. A nondestructive inspection apparatus fordiagnosing an internal defect of a measuring object by injecting anacoustic elastic wave into said measuring object, said apparatuscomprising: a vibrating section which is adapted to be placed inpressure contact with a surface of said measuring object for generatingsaid acoustic elastic wave; a receiving section which is adapted to beplaced in pressure contact with the surface of said measuring object forreceiving a reflected wave of said acoustic elastic wave; a pushingmechanism for pushing said vibrating section and said receiving sectionagainst the surface of said measuring object; a pushing forcemeasurement section for detecting pushing forces of said vibratingsection and said receiving section against the surface of said measuringobject during vibration thereof; a vibration control section for drivingsaid vibrating section thereby to generate said acoustic elastic wave;and a reception signal processing section for determining said internaldefect based on a reception signal from said receiving section; whereinsaid reception signal processing section comprises: a reflection energycalculation section for calculating a reflection energy level due toelasticity vibration of said measuring object based on said receptionsignal; a reflection energy correction section for normalizing saidreflection energy level by said pushing forces to calculate a correctionvalue; and an internal defect determination section for detecting saidinternal defect based on said correction value.
 2. The nondestructiveinspection apparatus according to claim 1, wherein said vibratingsection includes a magnetostrictive vibrator for generating saidacoustic elastic wave through a magnetostriction phenomenon.
 3. Thenondestructive inspection apparatus according to claim 1, wherein saidacoustic elastic wave comprises a chirp wave having a frequencycontinuously changing with time; said reception signal processingsection includes an envelope detecting section for determining anenvelope of elasticity vibration caused by the reflection of said chirpwave, said envelope detecting section being operable to calculate, basedon said envelope, a resonance frequency according to a naturaloscillation characteristic of said measuring object; and said internaldefect determination section detects said internal defect based on saidresonance frequency and a response waveform of a supply frequency of thevibrating section.
 4. The nondestructive inspection apparatus accordingto claim 1, wherein said internal defect determination sectioncalculates a distance to said internal defect based on a correlationbetween a distance to said internal defect and said correction valuewhich is prepared in advance.
 5. The nondestructive inspection apparatusaccording to claim 4, wherein the correlation between the distance tosaid internal defect and said correction value is stored in advance insaid internal defect determination section as map data of actualmeasurement values corresponding to said measuring object.
 6. Thenondestructive inspection apparatus according to claim 1, wherein saidreflection energy correction section calculates an additional correctionvalue by dividing said correction value by an abnormal range area ofsaid internal defect; and said internal defect determination sectioncalculates the distance to said internal defect based on a correlationbetween the distance to said internal defect and said additionalcorrection value which is prepared in advance.
 7. The nondestructiveinspection apparatus according to claim 6, wherein the correlationbetween the distance to said internal defect and said additionalcorrection value is stored in advance in said internal defectdetermination section as map data of actual measurement valuescorresponding to said measuring object.
 8. The nondestructive inspectionapparatus according to claim 1, wherein said measuring object comprisesa concrete structure.
 9. A nondestructive inspection apparatus fordiagnosing an internal defect of a measuring object by injecting anacoustic elastic wave into said measuring object, said apparatuscomprising: a vibrating means for generating said acoustic elastic wave;a receiving means for receiving a reflected wave of said acousticelastic wave; a pushing means for pushing said vibrating means and saidreceiving means against the surface of said measuring object; a pushingforce measurement means for detecting pushing forces of said vibratingmeans and said receiving means against the surface of said measuringobject during vibration thereof; a vibration control means for drivingsaid vibrating means so as to generate said acoustic elastic wave; and areception signal processing means for determining said internal defectbased on a reception signal from said receiving means; wherein saidreception signal processing means comprises: a reflection energycalculation means for calculating a reflection energy level due toelasticity vibration of said measuring object based on said receptionsignal; a reflection energy correction means for normalizing saidreflection energy level by said pushing forces to calculate a correctionvalue; and an internal defect determination means for detecting saidinternal defect based on said correction value.
 10. The nondestructiveinspection apparatus according to claim 9, wherein said vibrating meansincludes a magnetostrictive vibrator for generating said acousticelastic wave through a magnetostriction phenomenon.
 11. Thenondestructive inspection apparatus according to claim 9, wherein saidacoustic elastic wave comprises a chirp wave having a frequencycontinuously changing with time; said reception signal processing meansincludes an envelope detecting means for determining an envelope ofelasticity vibration caused by the reflection of said chirp wave, saidenvelope detecting means being operable to calculate, based on saidenvelope, a resonance frequency according to a natural oscillationcharacteristic of said measuring object; and said internal defectdetermination means detects said internal defect based on said resonancefrequency and a response waveform of a supply frequency of the vibratingmeans.
 12. The nondestructive inspection apparatus according to claim 9,wherein said internal defect determination means calculates a distanceto said internal defect based on a correlation between a distance tosaid internal defect and said correction value which is prepared inadvance.
 13. The nondestructive inspection apparatus according to claim12, wherein the correlation between the distance to said internal defectand said correction value is stored in advance in said internal defectdetermination means as map data of actual measurement valuescorresponding to said measuring object.
 14. The nondestructiveinspection apparatus according to claim 9, wherein said reflectionenergy correction means calculates an additional correction value bydividing said correction value by an abnormal range area of saidinternal defect; and said internal defect determination means calculatesthe distance to said internal defect based on a correlation between thedistance to said internal defect and said additional correction valuewhich is prepared in advance.
 15. The nondestructive inspectionapparatus according to claim 14, wherein the correlation between thedistance to said internal defect and said additional correction value isstored in advance in said internal defect determination means as mapdata of actual measurement values corresponding to said measuringobject.
 16. The nondestructive inspection apparatus according to claim9, wherein said measuring object comprises a concrete structure.